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The main purpose of this study is to investigate the bioaccumulation pattern and fate of heavy metals in duckweed‐based wastewater treatment ponds with different depth.

Three replicates of four reactors were used in this experiment. The reactors were randomly distributed on the bench and filled with 50 percent diluted sewage for the control reactors whereas diluted sewage mixed with 5 mg Pb/l and 5 mg Zn/l was used for the treatment reactors. The reactors were stocked with Lemna gibba at 1,000 g fresh weight per each square meter. The culture tanks were exposed to temperature range of 21‐25°C and light regime of 16 hours light using halogen lamps and 8 hours dark. The light intensity was maintained around 200 μ E m⁻² S⁻¹. The experiment extended for 30 days. Regular monitoring of the growth performance of duckweed was carried out with subsequent analysis of dry matter, heavy metals, phosphorous and nitrogen content. Composite samples from the water phase were subjected to the analysis of ammonia, nitrite, nitrate, orthophosphate and sulfate concentration. The analysis of sediment and biofilm were carried out at the end of the experiment. Interpretation of results was carried out using one‐way analysis of variance.

Statistical analysis showed a significant reduction in the growth rate of duckweed within the first five days exposure time. After five days exposure, the growth rate in the treatments returned to the normal growth till day 15 after which the growth became significantly lower in the small and medium scale ponds. The results revealed that zinc is more bio‐available than lead and both metals are mostly precipitated in the sediment probably as sulfides.

The results help in enhancement of heavy metals removal in a small anaerobic pretreatment unit before entering to the pond system by sulfate addition.

The results of the study confirm the positive effect of pond depth in reducing the heavy metal toxicity to the duckweed‐based wastewater treatment ponds.

The purpose of this paper is to evaluate the efficiency of a duckweed pond in the polishing of a stabilization pond effluent, as well as quantify its biomass production. Once an adequate destination is given to the produced biomass, the wastewater treatment plant can work in a sustainable and integrated way.

The duckweed pond consisted of a tank with volume 0.44 m³, operating in continuous flow with an outflow of 0.12 m³/day and hydraulic retention time of 3.8 days. Effluent samples were collected before and after the treatment, with analyzes made: daily-pH, dissolved oxygen and temperature; twice a week – total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (COD); and weekly – total solids (TS) and Biochemical Oxygen Demand (BOD₅). The duckweeds were collected each for seven days for its production quantification.

The highest efficiency of TN, TP, COD, BOD₅ and TS removal were of 74.67, 66.18, 88.12, 91.14 and 48.9 percent, respectively. The highest biomass production rate was 10.33 g/m²/day in dry mass.

There was great variation in biomass production, which may be related to the stabilization pond effluent conditions. The evaluation of the effluent composition, which will be treated with duckweeds, is recommended.

The evaluated treatment system obtained positive results for the reduction in the analyzed variables concentration, being an efficient technology and with operational simplicity for the domestic effluent polishing.

The motivation of this work was to bring a simple system of treatment and to give value to a domestic wastewater treatment system in a way that, at the same time the effluent polluter level is reduced and it is also possible to produce biomass during the treatment process.